---

#include <iostream>

struct Node {
    int data;
    Node* prev;
    Node* next;
    
    Node(int val) : data(val), prev(nullptr), next(nullptr) {}
};

class DoublyLinkedList {
private:
    Node* head;
    Node* tail;
    
public:
    DoublyLinkedList() : head(nullptr), tail(nullptr) {}
    
    void push_back(int val) {
        Node* newNode = new Node(val);
        if (!head) {
            head = tail = newNode;
            return;
        }
        tail->next = newNode;
        newNode->prev = tail;
        tail = newNode;
    }
    
    void pop_back() {
        if (!tail) return;
        if (head == tail) {
            delete head;
            head = tail = nullptr;
            return;
        }
        Node* temp = tail;
        tail = tail->prev;
        tail->next = nullptr;
        delete temp;
    }
    
    void print() {
        Node* current = head;
        while (current) {
            std::cout << current->data << " ";
            current = current->next;
        }
        std::cout << "\n";
    }
    
    ~DoublyLinkedList() {
        while (head) {
            Node* temp = head;
            head = head->next;
            delete temp;
        }
    }
};

int main() {
    DoublyLinkedList list;
    list.push_back(1);
    list.push_back(2);
    list.push_back(3);
    list.print(); // 1 2 3
    
    list.pop_back();
    list.print(); // 1 2
    
    return 0;
}